[Qemu-devel] [RFC PATCH v1 0/2] spapr: Abort when HTAB size requirement can't be met

[Bharata B Rao]

HTAB size is a factor of maximum memory size that is specified by maxmem=
command line option. In cases where there is shortage of host memory, host
will not be able to allocate contiguous memory for guest HTAB and will
instead allocate a smaller HTAB. This usually is not a problem but when
user starts hotplugging memory to the guest, we can run out of HTAB entries
and hence memory hotplug fails. This failure should have been handled
gracefully by the guest kernel, but currently it leads to guest kernel OOPS.
This will eventually get fixed when the handling of memory hotplug is
completely moved to kernel for PowerKVM.

Prevent such kernel failure by refusing to boot the guest when requested
HTAB size can't be allocated. However HTAB allocation happens in the
reset path from where it is too late to abort. Hence this patchset
moves the HTAB allocation to machine init and aborts if HTAB size
requirement isn't met.

This patchset applies against David Gibson's spapr-next. With this
patchset, simple boot, reboot and migration tests pass with HV KVM guest.
For PR KVM guest, boot and reboot tests were done since migration already
appears broken for PR KVM.

Changes in v1
-------------
- Correctly handle HTAB for PR KVM guests that use QEMU allocated HTAB.
- Verbose error message when aborting.
- Check for returned shift value in reset path too and abort when
  there is mismatch in htab shift values.
- Move the marking of htab_fd as stale from spapr_alloc_htab() to
  spapr_reset_htab() where it originally belonged.

v0: http://lists.nongnu.org/archive/html/qemu-devel/2015-09/msg05491.html

Bharata B Rao (2):
  spapr: Allocate HTAB from machine init
  spapr: Abort when HTAB of requested size isn't allocated

 hw/ppc/spapr.c | 42 +++++++++++++++++++++++++++++++++++-------
 1 file changed, 35 insertions(+), 7 deletions(-)

-- 
2.1.0